Cobalt-catalyzed intramolecular [2 + 2 + 2] cocyclotrimerization of nitrilediynes: an efficient route to tetra- and pentacyclic pyridine derivatives

[reaction: see text] In this paper, we wish to report the intramolecular [2 + 2 + 2] cocyclotrimerization of nitrilediynes catalyzed by the CoI2(dppe)/Zn system at 80 degrees C in CH3CN. Under these reaction conditions, various highly substituted nitrilediynes having steric conjunction at the alpha and beta positions to a nitrile group and a bulkier substitution at the terminal carbon of alkyne undergo [2 + 2 + 2] cocylotrimerization to afford tetra- and pentacyclic pyridine derivatives in good to excellent yields.     

HT G-四链体对甲基氮杂杯[6]吡啶的构象调控

甲基氮杂杯[n]吡啶(MACPn)是一类柔性、多构象的新型杂杯杂芳烃化合物,溶液状态中对其构象的调控与分离一直是此类化合物研究的难点之一。我们将DNA G-四链体作为功能分子,调控甲基氮杂杯[6]吡啶(MACP6)在溶液态的构象,结果表明,HT序列在K~+条件下所形成的混合结构的G-四链体可以诱导MACP6的手性构象,而在Na~+条件下所形成的反平行结构不具备此功能。一维核磁共振氢谱、分子对接与碱基突变进一步揭示了HT G-四链体与MACP6以边沿loop为位点的构型匹配作用模式,loop区增长,有利于HT G-四链体对MACP6的调控作用。本研究再次拓展了G-四链体作为氮杂杯吡啶构象调控功能分子的应用。     

A [4 + 2] cycloaddition strategy to pyridine boronic ester derivatives

Alkynylboronate cycloadditions of 1,4-oxazin-2-ones and 2-pyrazinones provide a direct and regioselective route to functionalized pyridine boronic ester derivatives.     

Rhodium catalyzed [4 + 2 + 2] cycloaddition and alkyne insertion: a new route to eight-membered rings

A novel variation of the rhodium catalyzed [4 + 2] reaction is reported. A catalyst system that forms an eight-membered ring product from the incorporation of an alkyne into a dienyne is discussed. The products are formed with high diastereoselectivity and in good yield. The highest yields are obtained with alkynes that possess either an oxygen or nitrogen in the propargyl position. Examples are presented where the tether between the alkyne and the diene contains three or four atoms.     

Synthesis of pyridone and pyridine rings by [4+2] hetero-cyclocondensation

Substituted pyridones and pyridines have been synthesised efficiently by employing iminium salt as a key precursor. These compounds were prepared using tandem [4+2] cycloaddition/deamination between azabutadiene and dienophiles.     

A [2 + 2] cycloaddition route to dimethylaminomethylene vinamidinium salts

[reaction: see text] Trifluoropropanoic acid reacts with 1 equiv of POCl3 in DMF to generate the trifluoromethyl enamine (7). At this stage, two reaction manifolds are available. The expected reaction with additional POCl3 generates the 2-trifluoromethyl vinamidinium salt (3c). However, thermally driven loss of fluoride generates an iminium ion, which sets the stage for a [2 + 2] cycloaddition to ultimately generate the dimethylaminomethylene vinamidinium salt (1).     

An efficient route to pyrimidine nucleoside analogues by [4 + 2] cycloaddition reaction

We report here an efficient synthesis for pyrimidine nucleoside analogues by [4 + 2] cycloaddition reaction. These compounds were obtained by convergent chemistry from glycosyl isothiocyanates 3a-f (pyranoses, furanoses, and dissaccharides) and diazadienium salt 5. In fact, diazapentadienium iodide 5 prepared from vinylthioamide 4 is an efficient intermediate in heterocyclic synthesis and reacts with isothiocyanates 3a-f affording beta-D-uracil analogues 7a-f in good yields and with total regiocontrol. All compounds were fully characterized by IR, HRMS, and 13C and 1H NMR (COSY and HMQC).     

DFT study on [4+2] and [2+2] cycloadditions to [60] fullerene

The functionalisation of C₆₀ fullerene with 2,3-dimethylene-1,4-dioxane (I) and 2,5-dioxabicyclo [4.2.0]octa-1(8),6-diene (II) was investigated by the use of density functional theory calculations in terms of its energetic, structural, field emission, and electronic properties. The functionalisation of C₆₀ with I was previously reported experimentally. The I and II molecules are preferentially attached to a C—C bond shared and located between two hexagons of C₆₀ via [4+2] and [2+2] cycloadditions bearing reaction energies of ?15.9 kcal mol^?1 and ?72.4 kcal mol^?1, respectively. The HOMO-LUMO energy gap and work function of C₆₀ are significantly reduced following completion of the reactions. The field electron emission current of the C₆₀ surface will increase after functionalisation of either the I or II molecule.     

Rhodium catalysed [2+2+2] cycloadditions- an efficient regiospecific route to calomelanolactone

A short regiospecific synthesis of calomelanolactone has been devised in which the key step is a [2+2+2] cycloaddition.     

Intramolecular ketenimine-ketenimine [2 + 2] and [4 + 2] cycloadditions

Bis(ketenimines), in which the two heterocumulenic functions are placed in close proximity on a carbon skeleton to allow their mutual interaction, show a rich and not easily predictable chemistry. Intramolecular [2 + 2] or [4 + 2] cycloadditions are, respectively, observed when both ketenimine functions are supported on either ortho-benzylic or 2,2'-biphenylenic scaffolds. In addition, nitrogen-to-carbon [1,3] and [1,5] shifts of arylmethyl groups in N-arylmethyl-C,C-diphenyl ketenimines are also disclosed.     

GaCl3-assisted [2 + 3] cycloaddition: a route to tetrazaphospholes

The GaCl3-assisted [2 + 3] cycloaddition of Mes*-N=P-Cl (Mes* = 2,4,6-tBu3C6H2) with trimethylsilylazide (TMS-N3) results in the formation of the first tetrazaphosphole, stabilized as a GaCl3 adduct in high yields (>96%).